1. Field of the Invention
This invention relates to plastic vehicle wheel covers with integral retention systems and more particularly to ornamental wheel covers that are retained on the lug nuts of the vehicle wheel.
2. Description of the Prior Art
Retention systems for ornamental wheel covers of the prior art require the use of multiple components in order to assemble the cover to the wheel. For example, in Spisak, U.S. Pat. No. 4,316,638, the wheel assembly includes metal retainers for bitingly engaging the sides of wheel attaching nuts to maintain the wheel in trim in position on the wheel wherein metallic retainer members have one end attached to the inside of a plastic hub cap, a mid-portion extending through an opening in the cap and an opposite end engaging the lug nut of the wheel to limit radial and axial movement relative to the ornamental cap in its mounted condition. Foster et al., U.S. Pat. No. 4,458,952, uses a round spring steel ring mounted on the inboard face of the wheel trim cover to engage in grooves in the wheel mounting lug nuts or the studs on which they are threaded to releasably retain the trim member on the wheel. The ring is mounted on the trim member such that the retention forces generated by the flexed ring are absorbed entirely by the studs and not by the trim member. Therefore, distortion and warpage of the trim member is avoided. In U.S. Pat. No. 5,297,854 to Gerald Nielsen et al. and the inventor of the present invention, Gregory Hauler, the wheel cover is secured to the wheel by the use of a plurality of metal retainers which are attached to the plastic cover. The metal retainers include a plurality of protrusions which act to engage the lug nuts and thereby attach the cover to the wheel.
Because of the high costs associated with multiple piece assemblies some prior art retention systems have attempted to provide a single piece design for a retention system to avoid the problems and costs associated with multiple piece designs. For example, U.S. Pat. No. 4,123,111 to Renz et al. discloses a retaining cover that is provided circumferentially in the engaging plane of the lug nuts with detents to engage the outer periphery of the lug nuts. The retaining cover has a shape that differs from the circular shape of the wheel cover exhibiting a relatively large lever arm between the connecting lines of the points of engagement of the lug nuts, thereby reducing the spring rate. The lug nuts are seated in recesses in the peripheral edge of the retaining cover. The edge of the retaining cover snaps in within the area of the recesses. To cover the lug nuts a wheel cover cap is provided that is mounted over the retaining cover.
Several problems exist with the Renz et al. device. Plastic is a relatively low strength material which tends to relax and/or creep over time and with temperature. Therefore, removal and replacement of the retaining cover could lead to loss of retention of the retaining cover to the lug nuts. The retaining cover is subject to stress and flexing in an area that is recessed and has a much thinner material thickness than the surrounding area of the cover, thereby making it subject to cracking. Expansion rates between the steel lug nut and plastic cover differ aggravating the above stated problems. Further, the fact that Renz et al. require a relatively large lever arm between the connecting points of engagement and the detent points in order to reduce the spring rate, it would not be possible to obtain this arrangement with shallow profile wheel covers. Further, the two-piece assembly provides large cavities between the retaining cover and the outer wheel cover in which mud and road debris can collect over time.
U.S. Pat. No. 4,382,635 to Brown attempts to overcome some of these problems by disclosing a wheel cover with integral retention fingers which is useable on conventional steel wheels. The cover is integrally retained on the wheel by the cooperating inter-engagement of tubular extensions of the cover mounting to the lug nuts. The extensions are axially slotted so as to be divided into a plurality of cantilevered fingers which cooperate with the lug nuts to retain the wheel cover thereto. The fingers of each extension include integral radially extending abutments which resiliently engage within a radial opening groove of a respective lug nut to resiliently grip the nut and retain the cover thereto. Concurrent with receipt of the abutments in the groove, a tapered radial face on each finger engages an axially outwardly extending annular face of the apertured embossment in an attempt to provide a slight axial outward force on each finger to prevent axial shifting movement of the extensions relative to the lug nuts.
The abutments describe a circle which is slightly less than the circle of the hexagonal portion of the lug nuts so that the fingers slightly separate or flex axially outwardly as the abutments move over the hexagonal portion of the lug nuts. Therefore, the fingers separate as the abutments move over an annular rib of the lug nuts until the abutments snap into the circumferential groove in each respective lug nut. When the abutments are received in the groove, the fingers return substantially to their normal molded shape. A radial tapered face of each abutment engages an axially outwardly extending annular face of the wheel surface to provide a slight axial outward force on each extension to prevent axial shifting movement of the extensions relative to the lug nuts.
One of several problems associated with this design is the adverse effects of tolerance stack ups between the axially outwardly extending annular face and the location of the groove on the lug nut. The fit of the cover to the lug nut depends on the depth and width of a groove that is on the lug nut and a tapered surface on the wheel face next to where the lug nut is seated. The tolerance build up among the radial tapered extension on the end of each finger of the cover, the lug nut, and the taper on the wheel's surface results in groove width variations that will prevent the radial tapered face of the abutment to move to the bottom of the groove, resulting in a loose fit on the lug nut and a stress condition in the fingers of the retainer, thereby subjecting the retainer to the problems listed above regarding the use of plastic.
Another problem associated with the lack of positive positioning in the Brown design is the potential for improper installation. It is possible, during attachment of the cover to the wheel, to apply a force that causes the cover to overtravel and press the fingers against the tapered wheel surface which in turn opens up the fingers, forcing them out of the groove and causing them to travel along the tapered wheel surface, which results in a loose fit.
Yet another drawback of the Brown design is a potential problem with the location of the circumferential groove on the lug nut and improper torque on aluminum wheels. It is known in the art that in order to achieve proper torque on the lug nuts for aluminum wheels, the conical seat must be deeper, providing more surface area contact with the wheel surface than required for steel wheels. The groove in the lug nut of the Brown design will prevent the lug nut from seating properly on an aluminum wheel by presenting less surface area contact with the aluminum wheel and thereby making it a problem to achieve sufficient torque for an aluminum wheel. In other words, the lug nut in the Brown design is not compatible with both steel and aluminum wheels.
A further problem is that the molding technique used to make the wheel cover of the Brown device results in the need to cover the molded body with an outer skin or cover in order to seal the nut wells that are made by the molding process. Again, a multiple piece wheel cover results in excessive additional manufacturing costs.
Because of the various problems identified with prior art retention systems, there is a need for a one-piece cover having an integral fastening system that provides positive positioning of the cover relative to the wheel thereby eliminating the effects of tolerance stack ups and the possibility of overtravel that result in poor fit of the cover to the wheel. There is also a need for a one-piece, low cost cover that attaches to the lug nuts with a fit that is independent of manufacturing tolerances outside of the physical dimensions of the nut itself, thereby eliminating the excessive variances that result from tolerance stack ups of several interrelated parts, i.e. the cover, the lug nut, the wheel surface, and the interrelationship of all three items. The cover attachment must not affect the lug nut torque or the contact interface between the lug nut and the wheel surface area so that a standard lug nut can be used for both aluminum and steel wheels.